I see no one replied. Did you figure it out?
Best way to see if water heater will light is to first (of course) turn on the propane. Silver valve on the tank. Then turn on your stovetop to bleed air out of the propane piping. Make sure you have good blue flame from the stove burners. Some orange at first is normal, indicates a little air in the lines.
Ensure the water heater has water in it (don't want to heat an empty tank). Easiest is to pull little lever on the pop-off valve on the tank itself, water should come out if full. Access this valve from outside the tank (open your door for hot water heater, drivers side of unit, little tab at top of door holds it shut). With switch inside the coach on, the flame tube should light and heat the tank. You may also notice a small switch inside the water heater access (from outside). That controls your 120VAC heat, it's located bottom left corner. When shore power is connected, and this switch is on, the tank heats with an electric coil. Purpose of this switch is to turn off electric heat when the tank is empty, like after winterization, etc. Don't want to burn up the coil.
So does the water heater light with propane? It will try three times, then you should cycle the switch inside the coach to get it to try again. If it try's, but does not light, there's several things to check, but I think I've written enough for one session